Guided by a social ecological framework, this application will consider individual-level risk factors (e.g., depressive symptoms) and the influence of social (e.g., partner/peer behaviors) and environmental (e.g., life stress) factors on changes in substance use in US Reserve Soldiers. Substance abuse is the most common health problem among veterans1 and substance use is linked to trauma, either in combat5 or at home.2 These issues are of heightened concern among the Reserve as they have more drinking problems5 and interpersonal conflict relative to active duty soldiers post-deployment.6 With more than half of the Military currently married, 1 it is important to examine the potential o a Reservist to influence, or be influenced, by his/her partner. Our previous research, 2-6 and that of others, 7-10 provides evidence that partner influences are powerful predictors of positive or negative changes in health. We also have found that peer networks are involved in changes in alcohol use among adults11 and that substance use shapes the peer network.12 Social/environmental influences may be particularly salient for Reservists and their partners as social networks change during deployments. These experiences are likely to strengthen the influence of a peer group, particularly if fellow soldiers are within one's peer networks post-deployment. Thus, the proposed study will examine individual and broader social environmental influences (e.g., relationship, community, and societal) on the association between stress and substance use for Reservists and their partners. Using a multi-wave design, Reservists and their partners (N = 400 couples) will be assessed 3 times over 2 years (i.e., baseline, Year 1, Year 2). Participants will be assessed using state-of-the-science Touch Screen Audio Enabled Computer Assisted Interviews. Using advanced longitudinal analyses (e.g., multilevel and GEE models), this proposal will examine: 1) changes in substance use (alcohol, tobacco, and nonmedical use of prescription drugs) over time in Reserve Soldiers and their partners on the basis of individual (e.g., depressive symptoms), relationship (e.g., partner and peer substance use), community (e.g., workplace/deployments) and societal (e.g., norms) factors; 2) the relation between stress/trauma (e.g., combat exposure/life stress) and substance use; and 3) how the integration of substance use into the relationship impacts marital aggression and dissolution. Importantly, each member of the couple will provide independent data. The proposed study is innovative in: 1) its focus on individual, partner, and peer influences; 2) its focus on Reservists and their partners; and 3) the application of an adapted social ecological model to a Reservist population. The proposed study is significant because it will add to our limited knowledge about the social (e.g., partner/peer influences) and environmental (e.g., stress/trauma) risk factors for substance use that are faced by Reservists. The knowledge gained from this conceptually and methodologically rigorous study will enhance the development of effective secondary prevention and intervention strategies to address the complex issues faced by military couples.